Due to the nature of the Bushmaster upper, you can't just swap out uppers to make it into a centerfire. Different hammer, different recoil system. Requires disassembly of stock to remove upper.

Upper bought used from Calgunner. Lower brand new until assembled to upper. Only put 100 rounds through this gun. This gun is tempermental about ammo. Runs well with CCI Minimags. Doesn't like cheap bulk ammo.